The present invention relates to the preparation and use of bio-oil as a preservative. More specifically, this invention is directed to the use of bio-oil as a wood preservative, either alone or in combination with other preservatives. Furthermore, this invention relates to methods for recycling wood preservatives treated wood products.
Wood preservatives are required to extend the service life of wood beyond what would normally be available if the wood was left untreated and exposed to the natural process of biodegradation. Presently, wood preservative fall into two basic classes: oil based and water based. The major oil based preservatives are creosote and pentachlorophenol (PCP). Copper, chromium, arsenate (CCA) is the most commonly used water based preservative.
There is an interest within the wood preservative industry to find an environmentally friendly means of treating wood products. Furthermore, there is a general lack of suitable disposal alternatives for treated wood taken out of service. Land filling of wood waste is the current disposal solution. However, wood is bulky, low density, and does not compact well in the landfill and there is a growing desire to find a solution to the treated wood waste problem and therefore increase the life span of the landfill.
The processing of carbonaceous feedstocks to produce heat, chemicals or fuels can be accomplished by a number of thermochemical processes, one such process being pyrolysis. Pyrolysis is character by the thermal decomposition of materials in the relative absence of oxygen (i.e., significantly less oxygen than required for complete combustion). Typically, pyrolysis refers to slow conventional pyrolysis whose equilibrium products included roughly equal proportions of non-reactive solids (char and ash), secondly liquids, and non-condensible gases. However, over the past two decades fundamental pyrolysis research has unexpectedly indicated that high yields of primary, non-equilibrium liquids and gases (including valuable chemicals, chemical intermediates, petrochemicals and fuels) could be obtained from carbonaceous feedstocks through fast (rapid or flash) pyrolysis at the expense of undesirable, slow pyrolysis products. In other words, the low-value product distribution of traditional slow pyrolysis can be avoided by the approach embodied by fast pyrolysis processes.
Fast pyrolysis is a generic term that encompasses various methods of rapidly imparting a relatively high temperature to feedstocks for a very short time, then rapidly reducing the temperature of the primary products before chemical equilibrium can occur. By this approach the complex structures of carbonaceous feedstocks are broken into reactive chemical fragments which are initially formed by depolymerization and volatilization reactions, but do not persist for any significant length of time. Thus, non-equilibrium products are preserved, and valuable, reactive chemicals, chemical intermediates, light primary organic liquids etc may be obtained.
Fast pyrolysis is an intense, short duration process that can be carried out in a variety of reactor systems. The common aspect of these reactors is the ability to achieve extremely rapid feedstock heating with limitation of the reaction to relatively short times by rapid cooling which stops the chemical reactions before the valuable intermediates can degrade to non-reactive, low-value final products. A fast pyrolysis process reactor system typically provides for a very rapid feedstock heating rate, typically within the range of 1,000. degree. to 1,000,000. degree. C. per second. The elevation in reaction temperature is controlled and lies within the range of 350. degree. to 800. degree. C. The reaction/residence time is also controlled and short and lies within the range of 0.03 seconds to 2 seconds. Fast pyrolysis is also characterized by a rapid product quench where the products are quickly cooled below 350. degree. C. within 0.5 seconds. An example of such a process is found in U.S. Pat. No. 5,792,340 which discloses the conversion of wood and other biomass residues to a non-viscous liquid product, termed xe2x80x9cbio-oilxe2x80x9d.
The processing of preservative treated wood via pyrolysis is possibly an option for recycling creosote or pentachlorophenol based wood preservatives. For example, U.S. Pat. No. 5,378,323 discloses the thermolysis of oil or tar based wood preservatives from sawdust and shavings obtained from the outer layer of treated telephone poles. The use of a fast pyrolysis reactor involving an inorganic particulate heat carrier for the recycling of these preservatives is not disclosed, nor are any of the properties of the product produced as a result of this process disclosed.
The present invention is directed to the use of bio-oil, obtained from the fast pyrolysis of wood biomass, as a preservative. Furthermore, bio-oil may also be mixed with traditional oil-based preservatives and be used either as a preservative carrier, or as an active ingredient within these novel compositions.
This invention also pertains to the recycling of wood treated with preservatives using fast pyrolysis to produce a bio-oil with properties suitable for use as a wood preservative. Results present herein demonstrate that bio-oil obtained from the fast pyrolysis of wood treated with creosote is as, or is more, effective than commercial grades of creosote.
Furthermore it has been noted that bio-oil adds to the strength of wood treated with bio-oil and acts not only as a preservative, but also to wood strengthening agent. Bio-oil also forms a protective skin on the exterior of the treated wood and acts as a physical barrier to decay.
The present invention relates to the preparation and use of bio-oil as a preservative. More specifically, this invention is directed to the use of bio-oil as a wood preservative, either alone or in combination with other preservatives. Furthermore, this invention is related to methods for recycling wood preservatives from treated wood products.
According to the present invention there is provided a bio-oil composition comprising derivatized lignin, alcohol, natural organic acids, carbonyls that is liquid at room temperature, wherein said bio-oil exhibits properties of a preservative. This bio-oil composition may further be characterized in comprising 2-methoxy-4-methylphenol and 3,4-dimethoxybenzoic acid.
This invention is also directed to a wood preservative composition comprising the bii-oil composition as defined above and a water based, or an oil based, or a combination of a water based and an oil based preservative. Preferably the bio-oil composition comprises an oil based preservative. Furthermore, it is preferable that the oil-based wood preservative is selected from the group consisting of creosote or pentachlorophenol.
This invention also embraces a wood product treated with any of the bio-oil compositions as defined above.
This invention also relates to a method of preparing a wood preservative composition, the wood preservative composition comprising the bio-oil composition as defined above and an oil based preservative, the method comprising processing wood treated with the oil based preservative using a fast pyrolysis reactor, and obtaining the resultant bio-oil fraction. Preferably, this method uses wood treated with creosote or pentachlorophenol as the feedstock for fast pyrolysis. This invention is also directed to a wood product treated with the wood preservative composition as defined above.
This invention also embraces a method of preparing a wood preservative composition comprising, heating bio-oil and adding a waterbased, or oilbased, or a combination of a water based and an oil based preservative to the bio-oil, followed by cooling the wood preservative composition to room temperature.
The present invention also provides a method of sealing a wood product comprising treating said wood product with any of the bio-oil compositions defined above.
This invention also relates to a method for increasing the strength of a wood product comprising treating the wood product with any of the above bio-oil compositions.
This invention also embraces a method of recycling preservative-treated wood products comprising:
i) processing the preservative-treated wood products within a fast pyrolysis reactor;
ii) obtaining a bio-oil fraction; and
iii) treating a wood product with said bio-oil fraction.
Furthermore, steps i) to iii) this method may be repeated.
The present invention is directed to the use of bio-oil as a preservative agent. Furthermore, this invention is directed to novel bio-oil compositions that are effective in wood preservative applications and exhibit several desirable properties including increased preservative qualities, increased wood strength, the formation of a protective coating of the wood product, and pleasant wood colouration. Furthermore, this invention provides for a method of recycling treated wood products and demonstrates the suitability of the re-use of the resultant bio-oil product within preservative applications.